The present invention relates to a method of assembly for a pressure gauge in which a rigid safety plate, preferably metallic, has the Bourdon tube and the associated gear mechanism mounted on one side and the gauge dial and pointer mounted on the other side, so as to provide protection for the observer of the gauge in the event of a Bourdon tube failure or rupture. More specifically, this invention relates to a method for installing a preassembled and calibrated unit in a gauge case or housing, which includes a safety plate having the Bourdon tube and gear mechanism mounted on one side and the gauge dial and pointer mounted on the other side. This new and useful method offers particular utility in that it provides an economical method of gauge construction, especially when used in conjunction with the apparatus of the invention for mounting a viewing window on a pressure gauge case, disclosed and claimed in the copending application, Ser. No. 772,209, filed Mar. 14, 1977 and assigned to the same assignee.
Pressure gauges employing a Bourdon tube frequently are utilized for the measurement of very high pressure gases and liquids, for example, on the order of several thousand pounds per square inch. Dynamic changes in the pressure of the fluid or gas under measurement cause expansion or contraction of the Bourdon tube, and this movement is transmitted through a gear mechanism to a pointer or indicating needle that moves in relation to a graduated gauge dial. The term "gauge movement", as used herein, refers to the Bourdon tube, gauge dial, pointer and gear mechanism.
There is always the possibility of a Bourdon tube rupture from an over pressure condition. If this happens in a gauge without a safety plate, as defined below, the fluid or gas in the tube and the gauge movement may be propelled from the interior of the case, and some of these parts may shatter the viewing window. Therefore, it is desirable to employ a safety plate to block the path from the Bourdon tube and gear mechanism to the viewing window. The safety plate frequently is constructed of metal and is integral with the gauge case. For example, in FIG. 1 of U.S. Pat. No. 3,141,335, the safety plate 14 is an inwardly extending portion of wall 10. Assembly of the gauge consequently requires mounting the Bourdon tube 18 and gear mechanism on one side of the safety plate 14, and mounting the related pointer and dial on the other side. This particular approach presents several distinct disadvantages.
The case construction is more expensive, and assembly and disassembly of the gauge movement is unduly complicated, as it necessitates removal of the gage movement from both ends of the case.